1. Field of the Invention
The present invention relates to a capacitive sensor, and more particularly, to a capacitive sensor having a pair of spaced polymeric conductors, wherein a substantially constant spacing between the polymeric conductors is maintained by a non conductive web.
In a particular configuration, the present invention relates to a trapping protector for detecting the presence of an object in a sensing region. The trapping protector can be employed in a weatherseal, and comprises a capacitive sensor having a body, at least one polymeric conductor as a ground electrode and at least one polymeric conductor as a sensor electrode arranged in a spaced apart relation and embedded in the body, wherein an intermediate insulating web maintains a substantially constant separation distance between the conductors along the length of the sensor. Preferably, the separation distance between the polymeric conductors is substantially maintained during installation of the trapping protector, such the separation distance in the installed sensor is substantially constant along the length of the sensor.
2. Background Art
Capacitive sensors have been employed in motor vehicles. Specifically, the number of vehicles equipped with a power-driven window or sunroof is increasing, which utilizes the driving force of a motor whereby a light touch to an operating switch permits easy opening and closing of the window or sunroof. However, there exists the danger that foreign matter or a body part can be caught between the upper edge of the window and the window frame upon closing, thus leading to injuries. National Highway Traffic Safety Administration Standard 118 contains regulations to assure safe operation of power windows.
Several approaches have been made in order to avoid such injuries. U.S. Pat. No. 5,459,962 discloses a trapping protector comprising two mutually spaced apart electrical conductors initiating a switching process of a drive unit when brought in contact. U.S. Pat. Nos. 5,754,017, 5,932,931 and 5,966,071 teach a power-driven window comprising a load detecting means for detecting the drive load of the motor driving the window. These trapping protectors require physical contact and cause significant squeezing of a body part caught between the upper edge of the window and the window frame. Amended Standard 118 states that the maximum force allowable during closure is to be less than 100 Newton onto a solid cylinder having a diameter of between four and 200 millimeters.
There have been proposed trapping protectors which do not require physical contact and, accordingly, do not cause squeezing. U.S. Pat. Nos. 4,453,112 and 5,621,290, the disclosure of which is incorporated by reference, teach capacitive sensors. Arranged on a window frame is at least one sensor electrode to which an alternating current is applied. As soon as an electrically conductive medium such as a human body part is near said sensor electrode the capacity between said sensor electrode and a ground electrode changes. The change in capacity changes the frequency of an output signal of the sensor electrode. The change is compared to a reference level, and the motor for the window is stopped or reversed if the change exceeds the threshold. The capacitive sensors can only detect dielectric materials. However, wood, plastic or any other non conductive material cannot be detected as they do not cause a change of capacity.
The need exists for a capacitive sensor that can provide a sufficient signal to allow sensing of objects within a sensing field of the sensor. The need also exists for a capacitive sensor that can be integrally incorporated into a seal or trapping protector. The need further exists for a capacitive sensor that can be cooperatively engaged with a seal or trapping protector after formation of the seal or trapping protector.